Hey Sam! Sorry to bother during an exciting book launch, but it jogged my memory. Has the situation with the costs of ISBN changed since you described your purchase? There's a lot of moving parts in the USA, so I figured I'd ask since you've glanced at it more recently. Thank you and fair sailing!
Not to my knowledge -- I just checked and it looks like they're still quite expensive in the US, although there appears to be a new option to purchase 10 for $295. Previously it was either 1 for $125 or 100 for $575 with no in-between. On the plus it doesn't look as if prices have increased at all.
I bought 100 a few years ago and have about 80 left. They aren't transferrable; I can't sell them on or give them away. Any book published with one of my ISBNs is defacto published by Extribulum Press. I've considered actually opening Extribulum to other authors, because in theory I could be a publisher, but I haven't really found anyone interested and I would also want to vet any book that goes out under the imprint.
But every book I publish uses two and some use three (paperback, epub, hardback) so this will cover 30-40 books, roughly, and I figure I've got that many left in me. :D even if I never print another one, I've already saved over a thousand dollars not buying them individually, so the investment was worth it.
You don't need an ISBN to print a book, of course, but most libraries and bookstores need your book to have one in order to stock them, so it's not ideal to print without one. Many self publishing platforms (such as Lulu, which I use) will give you one for free if you list them as the publisher, but that means they retain certain legal rights to the published matter and I just was never comfortable with that. Worth it to me to have complete legal ownership of all of my books, just in case.
